text:
Why did fly-by-wire systems take so long to implement?
The first commercial FBW airplane was the Airbus A320, which was introduced in the late 1980s. This system only worked after decades of research by American and European aerospace companies. If FBW only converts mechanical motions from an airplane's control yoke into electrical signals (along with sensor feedback), which change the aircraft's control surfaces, what caused FBW to be implemented so late, besides the abundance of computers even before the A320? Can someone also check my understanding of FBW?
My understanding of FBW:

Aircraft manufacturers use rotary encoders and potentiometers to translate mechanical changes in the control yoke into electrical signals.
The FBW computer(s) use feedback from the aircraft's sensors, and compare it with the pilot's input. A derivative based FLL system is used, perhaps?
Hydraulic valves/servo motors are used by the FBW system to change the state of control surfaces.

Thank you.

"If FBW only converts mechanical motions from an airplane's control yoke into electrical signals (along with sensor feedback), " If this were true, then why fly by wire?

A simple answer is that the aircraft control system has ultimate responsibility for survival of the aircraft. If it completely fails, you are as good as dead in most cases. Short of in-flight destruction, hardly anything can be worse.
Thus, full-authority (i.e. without mechanical backup) FBW gained acceptance only when the confidence in its overall reliability was sufficiently high. Naturally, it appeared on military airplanes first, where demands to reliability can be lower (the pilot can eject, after all), while demands to the control system sophistication are often higher.
(Others have already commented that A320 wasn't the first commercial airliner with FBW; Concorde had it much earlier. As for your understanding of FBW, it's basically correct. Sometimes, strain gauges rather than potentiometers are used as control stick sensors: force as the primary input is generally better than displacement).

A fighter jet also has reduced liability problems--a complete failure is likely to kill one or two people; a failure on an airliner is more likely to kill hundreds of people.

@JerryCoffin not to mention that those one or two people are military and thus have accepted the fact that they could die in mission.

@Berend, the question was not "why use FBW"; it was "why did it take so long to adopt". Listing the advantages is tangential to the question. // Safety requirements are lower for military aircraft; apart from just formal requirements, they usually have the last option should this critical system fail, and are risking two orders of magnitude fewer lives (in peace time) per hour.

In truth, ANY kind of advancement in aviation technology is usually met with a lot of skepticism and reluctance to implement - composite structures, jet propulsion - you name it.  They all were available for at least a decade prior to widespread acceptance.  And for good reason.  If your design fails, it crashes and the people on board all die.  If you are an OEM, that could cost you business, you could be sued into bankruptcy, and, if a jury feels your actions in the design of this vehicle constitute criminal negligence, you could face prison time.
Aircraft design has been ruthlessly shaped by natural selection over its 115 years of history.  Early designs which didn’t work often had lethal consequences and the few which were successful quickly became standards by which all future vehicles were based upon and manufacturers quickly learned not to stray too far from these successful templates.  Some of this can be attributed to an immature state of aerodynamics in the early days, but a lot of it is just the risk of implementing an immature technology that hasn’t been fully vetted and its benefits and drawbacks cannot be fully anticipated.
Fly by wire is now a very mature system thanks to pathfinders like Airbus and General Dynamics, but in the early 80s, when the A320 was designed, it was not widely used, save for a few experimental and military aircraft; all of which went through pretty bumpy development paths to perfect.  Design a fighter with a Fly-by-Wire control system?  Sure.  And if it goes down, only one person goes with it.  As small airliner with an FBW has a design fault which the OEM did not anticipate, over 100 passengers perish and the company reputation goes to zero.  Fortunately the gamble paid off for Airbus.

For two reasons:

The main priority of flying is staying in the air: Fly By Wire first had to prove that it was as safe as fly by pulling a stick.
When aircraft were slower and the control tasks more straightforward, humans could do a pretty good job: there did not seem to be a problem to solve.

Technically, Fly By Wire means that there is no direct mechanical connection between the flying controls and the control surfaces. If there is, the human in the loop determines the extent of surface deflection - the aircraft response as sensed by the human sensory organs will then determine further action. Humans have some pretty useful feedback sensors:

Very accurate and fast force sensors in the fingers.
Accelerometers in the inner ear, rapid response but very limited sustained accuracy.
Velocity sensors in the peripheral vision field, slower repsonse but better accuracy than the inner ear.
Accurate and sharp position information in the central vision field.

The pilots can use their built-in sensors to fly the aircraft according to their trained control behaviour - but if they make a mistake they can rip the wing tips off. Fighter pilots want to pull as many g's as the airframe can take, and had to learn this by calibrating their bums. Penalty for over-commanding the load factor was an uncontrolled crash, the enemy wins.
So it makes sense to add mechanical sensors, and to limit the control surface deflections such that the known structural limits are not exceeded: the F-16 does not allow for control surface deflections that would cause a load factor > 9g, the A330 deflects spoilers when it senses > 2.5g. In other words, it makes sense to add artificial intelligence to the control loop. The human-in-the-loop can then concentrate on the main control task, without having to add safety margins.
High-tech flying had a requirement for a higher tech solution than only a human: outmanoeuvring the enemy, or exceeding the natural human error limit for repetitive tasks. We can now add intelligence to the systems while improving overall safety numbers, half a century ago we couldn't. And we can still make the argument: do we always really need it? The B737NG has the same excellent safety record that the A320 has...

"In other words, it makes sense to add artificial intelligence to the control loop." What you describe isn't AI, it's limiting systems with a fixed, predetermined limit. An AI would be more (but not quite) like, it'll let you do a little more and see if the plane stays in one piece; if it does, then fine, if not, then back off slightly on the allowed loading for next time. Not a great idea when the failure scenario potentially includes "crash and burn" (literally).

The base-line of FBW is that the steel-cables that link the cockpit controls to the hydraulic jacks are replaced with copper-wires carrying (usually) a voltage which encodes to a desired control-surface position. Notice that there are NO computers in this definition of FBW.
But once you have an electrically-signalled flight control system, then you can introduce computers to interfere/reduce/increase/modify the electrical signal according to some rules (aka "Laws") in order to achieve something. This inclusion of computers is what most people understand by FBW.
Notice that you could remove the computers from the system (eg by failures) and you would still have an electrically-signalled flight control system which is fully flyable (usually known as "Direct").

Because there was no point in it until a computer with significant performance could be included in the loop! And those were not available, in sufficient quantity and quality, earlier.
The control surfaces of large aircraft have to be operated hydraulically, because that's the only kind of actuator that provides all of the precision, force and fast response times required. These can be connected directly to the control column via hydromechanical power drive, which is relatively simple and well understood. And since the hydraulic systems are pressurized with central pumps, the hydraulic lines have to run around the plane anyway, so there is nothing to be saved by inserting an electrical signalling in between.
Adding electric transmission only gains any benefit at the point there is a computer that can modify the commands to provide additional functionality—flight envelope protection and (in Airbus) automatic trim.
These functions could only be implemented at the point where processors became available that had sufficient performance and were produced and used in large quantities so their reliability was confirmed in practice. And at that point, it took considerable time to develop the control software and thoroughly test it. This kind of application requires qualified estimate of mean time between total failures at least 10⁹ hours, which means a couple of backup solutions and a lot of testing for each level.

There was a case being made in the late 80s for local small pumps near the hydraulic actuators, eliminating the lengthy hydraulic lines with associated pressure losses.

The first real FBW system was probably the one put on the F16... to increase maneuverability, the aircraft was designed to be unstable in flight, so the FBW was necessary to keep the plane flyable. In that case, there was a compelling reason to develop FBW: a more maneuverable combat aircraft. Also, that system was ported to the F117, which had such atrocious aerodynamics that it, like the F16, was essentially unflyable without computer assistance.
In commercial aviation, the case is far less compelling. And it hasn't been an easy path. The very first A320 ended up landing in a forest, when it's flight computer mistook a slow flyby at an air show for a landing cycle. Oops... There have been several crashes traceable directly to FBW or sensor malfunctions (XL Airways/Air NZ acceptance flight, AOA sensor froze up) and Air Asia 8501, an A320 that crashed due to high altitude stall brought on by a malfunctioning rudder position sensor , to sensor malfunctions combined with different flight control layout, plus maybe fully automated aircraft lulling pilots into complacency (AF447, pitot tubes froze, bad sidestick design, inexperienced pilot), to just plain confusion in the cockpit working with FBW systems (Air Inter confusion setting descent rate, flew into a mountain).
Plus non fatal incidents that could easily have become fatal, like Qantas 72, where the inertial reference unit started sending weird data to the flight computer, sending the plane into a series of uncommanded dives and ascents.
FBW was supposed to make flying simpler, when in truth it just trades one set of complexities for another.
They have been slow in coming in commercial aviation because the advantages to airliners (who don't need more maneuverability or stealth capability) aren't nearly as compelling as they are on military aircraft, while the consequences of failure tend to kill a lot more people. If the FBW computer malfunctions in a military aircraft, the pilot punches out and has about an 85% chance of surviving. Airliners don't have that option.

The A320 FlyByWire system has also prevented many mishaps from happening that would be possible in a conventional control system. Safety numbers are very good for both A320 and B737 latest types. Why don't you compare the safety numbers of the 737 Classics with the early A320. Very one-sided answer.

The very first A320 ended up crashing in a forest, with the FBW system saving most occupants by preventing full stall. The stunt they attempted would have ended way worse without the alpha-limit. Of course they wouldn't have attempted that stunt if the alpha-limit wasn't there, because they wouldn't try to show it off, but you can't really blame that on the system.


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Can a completely drained battery be recharged via ground power on an airliner like the B737?
When accidentally leaving the battery switch or something powered by the hot battery bus on over night, an aircraft's battery could completely discharge. Normal startup, where the battery is switched on first and then external power is connected, would no longer be possible.
Is it possible to somehow connect an external power unit to the aircraft such that the drained battery is being recharged? Or would maintenance have to swap out the battery or charge it in some other way?

Details for the Boeing 737 are below, but answers for other airliners are welcome:
On the Boeing 737 NG, the batteries are charged via their own transformer rectifier units:

Battery Charger Transformer/Rectifier
The purpose of the battery chargers is to restore and maintain the batteries at full
electrical power. The main battery charger is powered through AC ground service
bus 2. The auxiliary battery charger is powered through AC ground service bus 1.

(Boeing 737 NG FCOMv2 6.20.12 - Electrical - System Description - DC Power System)
These ground service buses can be turned on independently of the main aircraft AC buses:

Ground Service
For ground servicing, a ground service switch is on the forward attendant’s panel.
The switch provides ground power directly to the AC ground service busses for
utility outlets, cabin lighting and the battery charger without powering all airplane
electrical busses. The ground service switch is a momentary push button and is
overridden when both AC transfer busses are powered.

(Boeing 737 NG FCOMv2 6.20.2 - Electric - System Description - Electrical Power Generation)
This sounds like the battery chargers could be powered via ground power in ground service mode. It is however not clear to me, if this push button would even work without any battery charge left.

Wet cell NiCads that most airliners use can suffer from "thermal runaway" when charging, for a range of reasons like overcharging, bad connections, low electrolyte, excessive ambient temperature, cell polarity reversal, etc.A high charge rate and an ambient temperature over 100F during charging can trigger a thermal runaway. If a battery is completely depleted, it needs to be carefully monitored during recharging to control temperature and cell condition. Much safer to remove it and take it to the special battery room to be recharged, so if it blows up it just makes a mess in the battery room.

Surprised this isn't from "Sean" :)

@Harper-ReinstateMonica Sorry, no footnotes :D

I now have this image stuck in my head of two 737's, parked nose to nose, with two huge jumper cables between them :)

Are you asking for an APU (Auxiliary Power Unit)?

@Mast No, the APU can for sure no longer be started with a drained battery (see the "TO APU STARTER" in the diagram above, or Ralph's story). I am asking about a GPU (Ground Power Unit), also called external power.

@Harper-ReinstateMonica: Wish I had thought of this one!

My one experience with this was in a 737-300 that had the battery charger die, and the battery depleted while in flight.  The Battery Bus was still powered by TR3, but the Hot Battery Bus died (interestingly, not a scenario I'd ever seen in the simulator).  We got to the gate & couldn't start the APU and couldn't connect ground power, so when we shut down both engines, we immediately had "one blue light" -- i.e. ground power is plugged in & available, but NOTHING else -- dark airplane.
I don't recall how longer after that it was, but we eventually were able to connect ground power, probably to the ground service bus first.  Then, with the ground service bus powered, the battery would recharge.  I don't recall if we were able to get anything beyond the ground service bus powered after that.  (Presumably, if the battery recharged enough, we could have gone back to normal routines.)
As a practical matter, though, our maintenance does exactly as John K mentioned: if the battery has been depleted, it gets replaced.  How much of that is a matter of what happens during charging, and how much of that is concern about damage to the battery itself, I don't know, but in practice they won't use the aircraft's battery charger in the manner suggested in the OP.  (The battery charger brings it back up to full charge after things like starting the APU or running on battery power for the time between initial power-up and when APU or ground power are connected -- but that's a long way from being fully depleted.)

I worked on NICAD aircraft batteries in the USAF. Batteries are compose of multiple cells. as the battery discharges and gets near 0 volts, one or more of the cells may actually reverse its potential. One it has reversed it cannot be easily recharged. We would apply a load to drain the cells monitoring each and when it reached near zero volts, it get shorted out. Once all cells are shorted out, and have cooled down, the shorts were removed and the battery charged, carefully monitoring the voltage of each cell. Some time a depleted cell would not recharge and it was replace.

You ask "would it be possible".
The answer is, with certainty, yes.
"Is it done?" is another matter.
John DeVries notes that " ... the external power contactor requires battery power to close. Dead battery, no ground power."
I note below that this is by conscious design choice - ie the choice that has been made is that the aircraft cannot be powered up from an external source if the battery is 'flat'. Technically it's possible.

I can answer this from a "how it is almost certainly designed to be" basis.
Note that this applies to the situation that you described - with the aircraft on the ground, with the engines (presumably) not operating, and the battery not being charged from external sources. As Harper ...  notes, if this situation occurred in flight the decision may be to risk damaging or destroying the battery if this increased the prospect of not destroying the aircraft.
The block labelled "BAT" on your diagram is not just a battery but a battery subsystem with its own protection and management capabilities.
I'm an electronic designer.
I would expect with near certainty that Boeing (and any airline) would do what any competent designer would do, and

Be utterly certain to use a design that would automatically disconnect the battery when a minimum safe voltage was reached so that the battery would not be in any way damaged by 'running it flat'. Such a system would be wholly unable to be bypassed by any manual or intended automated action. Only a fault condition within the battery subsystem (labelled "BAT" on your diagram) would allow otherwise. Such a fault is of such seriousness that it would be protected against separately and any condition which sought to cause it would be both prevented and reported on.

Arrange the battery to be in a condition such that if it was ever able to be charged in place by external power then it would be able to be when flat.

Make design decisions that suited their operating procedures.

Recharge from flat would definitely be technically possible, but it may not allow recharge from flat because any event that allowed this state to be reached indicates a systems failure (whether due to human factors or other) that would make it deemed-unsafe to trust the battery state (even though the battery would almost certainly be undamaged).

Powering up in a battery-less state from an APU or other source is "just a matter of design. It can be done if desired. Whether it is able to be done depends on high level system design considerations, and not technical ones.

I wouldn't necessarily presume Boeing would protect the battery at the expense of aircraft function.  A similar case is a diesel emergency fire pump; they don't have low-oil or low-water trips because the engine tripping out in the middle of a fire.  The engine is expendable if it gets the fire out.

@Harper-ReinstateMonica I agree with your point - but/and note that it lies outside the scope of what the OP intended. Low battery in flight due to loss of in flight charging would place it in your scenario. Hopefully there would be a detected and staged reduction in battery use if such a scenario eventuated.

You probably assume there is a micro controller present. But 737 first flew in 1967. In some old aircraft this battery manager may not be so capable of of.

@h22 Good point, but the same rules apply when it comes to battery design in mission critical applications (and anything serious). I'd been 'playing' with electronics for about 5 years by then :-).  2years & 3 months and a few weeks before the 1st moon landing.
I imagine that the battery system may have been somewhat upgraded in the intervening 53 [!!!] years. || FWIW - congratulations on making a good point politely rather than making the recipient feel put upon :-) - often a bit of a lost art on the 'net these days.

It is correct that the battery charger will work on the ground service bus, but the external power contactor requires battery power to close. Dead battery, no ground power

So there is no way to close this contactor manually?

Nice to know. A design choice.

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For CG calculations, where is the root chord located on a swept wing aircraft?
With a swept wing aircraft (specifically a MiG-25 I am modelling) where is the root chord taken from to calculate the location of CG?
Is it the root chord of the wing (where it attaches to the fuselage) or a projected line extended from the the leading / trailing edge to the centreline of the fuselage?

Hi and welcome to the site! I have edited your question a bit to make it clearer, you can roll back to edit if you meant it differently.

It's expressed in Mean Aerodynamic Cord. On a swept back wing, you can construct it as follows.

Hi. Many thanks.

The centre line of the aircraft is used regardless of the fuselage width? eg if the aircraft has a really wide body and stubby wings, the centreline of the fuselage is still used for the calculation?

@LeeCowen Not sure I understand your question.

Sorry - i'm not explain myself well. I will try to put it another way. If two aircraft have the same size and shape swept wings, but one aircraft has a wide fuselage so the wings are far apart, but the other has a narrow fuselage so the wings are closer togehter, would the CG be the same place on both?

Oh OK. CoG of the fuselage would be at the same (X,Y,Z) location. CoG of each wing would have the same X and Z location. Each wing would have an offset in Y-direction, one has $ \Delta Y $ and the other $- \Delta Y $ which cancel each other out...so yes, the total CoG would be at the same location.

Superb. Many thanks.

For CG calculations on swept wing aircraft you don't use root cord, you use mean aerodynamic chord or MAC. To calculate the MAC:

Identify the center of gravity location, in inches from the datum.
Identify the leading edge of the MAC (LEMAC), in inches from the datum.
Subtract LEMAC from the CG location.
Divide the difference by the length of the MAC.
Convert the result in decimals to a percentage by multiplying by 100.

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Do crew rest seats count towards the maximum allowed number of seats per flight attendant?
We work as flight attendants on a 737-400. We were taught that we must have one FA per 50 seats. Normally our planes have 150 seats and with three FAs we have no issues.
Recently the seat configuration was 152 seats. We called our company and told them that we were not legal to work like that since there were only 3 of us. They stated that 2 seats were for "crew rest" and that we were legal as long as we didn't seat passengers in those 2 particular seats. Is this correct? No one ever said anything said to us about these crew rest seats.

Welcome to aviation.SE! This question is related but doesn't address the crew rest seats point.

How many seats on the airplane are proffered to passengers (i.e. have a seat number that is conceivably issuable on a ticket).

The applicable regulation, CFR121.391, says this:

(4) For airplanes having a seating capacity of more than 100 passengers—two flight attendants plus one additional flight attendant for each unit (or part of a unit) of 50 passenger seats above a seating capacity of 100 passengers.

Note that the regulation only refers to seating capacity, not whether or not the occupants are "passengers" under the legal definition (fare paying person), or airline employees.  With 152 seats, that airplane has 2 seats, a part unit, of the next "50 seat unit" above 150 seats. So I would say your concern is correct and you need an extra FA to be compliant with 121.391, or at least I would assume so until the airline is able to show that the seats are not counted as "passenger capacity" due to some language in its operating certificate or some other document.  Probably something for your union's legal rep to confirm.

indeed, deadheading crew count as passengers for the FA's primary mission: safety.

But it says "passenger seats" and these are crew seats.

I would say if the seats are in a zone placarded "crew rest area", or are outside of the cabin area pax normally sit, yes they can be designated crew seats.  But if they are just two extras in the main cabin, that's a problem.  If passengers COULD be sitting there, the seats have to be considered part of the passenger capacity.

This is probably a dumb question, from a non-aviator, but would the pilot seat(s) be considered a passenger seat as well? Or is there specific language reserved for pilots? Would that same language cover crew seats?

No crew seats are crew seats. A passenger is a legally defined entity (fare payer) and can't legally sit in a crew seat.  And in fact airlines separate crew from passengers in the weight and balance calculations.  Crew are "built-in" you might say, to what is called "Basic Operating Weight", which is empty weight plus standard crew.

So even when a plane flies half-empty, do they still need a full crew?  (I know they generally try not to do that, but I've been on some pretty sparsely-seated flights before.  Didn't think to count the FA's...)

I would have to agree with David here. The regulation says "passenger seats." Crew seats are not passenger seats, regardless of what form they may take. Whether it's a jump seat, a blocked-off economy-style seat, a crew rest bunk, or a full-on flat-bed business-class seat that is blocked off for crew rest, a crew seat is a crew seat, not a passenger seat.

@DarrelHoffman Yes, they still need a full FA crew when flying half-empty. However, if they're flying completely empty on a ferry flight (e.g. to/from a maintenance base or similar,) then a cabin crew isn't needed.

I have heard this happening in other airlines, so I presume its legal. If the seats are placarded "crew use only", the passenger capacity of the aircraft is considered to be reduced.

Yes good point.

So if a 150-seat aircraft is only 60% booked, can the airline placard 50 seats as crew use only and reduce the number of FAs by one?

@MikeScott If you did that the regulator would likely complain. However in this case, they're medium-term disabling 2 seats. If the regulator were to complain, they'd just physically remove the seats and the net effect, in terms of safety, would be identical. These things are often up to the judgement of the regulators.

The seating capacity as written in the registration document is all that matters.
There can be more seats installed, but the aircraft is not legally permitted to carry more passengers. Aircraft are often registered with lower seating capacity, MTOW or ETOPS than certified to reduce crew/maintenance requirements and airport fees. A web search for the tail number will likely tell you the registered seating capacity and MTOW.

What's your source for these claims?


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Do leading edge flaps increase the critical angle of attack?
So from my understanding, trailing edge (TE) flaps increase wing area + camber, effectively increasing the coefficient of lift for a fixed AOA which leads to higher lift at a fixed airspeed and AOA. This allows an airplane to fly at lower speeds + lower AOA to maintain lift.
But does the same also apply to leading edge (LE) devices like slats or flaps? I know that a slat moves to allow underside air to flow over the top and prevent airflow separation, leading to a higher critical AOA. Do LE flaps also increase the critical AOA? Also, it seems that both slats and LE flaps affect the wing camber, increasing it. Does this mean that their deployments lead to higher coefficients of lift for a fixed AOA like with trailing flaps?

Welcome to Av.SE!

Thanks, happy to be here!

May be this is helpful: https://en.m.wikipedia.org/wiki/Leading-edge_slat

And may be this too:   https://aviation.stackexchange.com/questions/25920/what-is-the-difference-between-a-leading-edge-flap-and-a-slat

Yes leading edge devices indeed postpone stall to a higher Angle of Attack. They are particularly useful for:

Airfoils which are prone to leading edge stall. Deflection of the trailing edge flap creates upwash at the wing nose, which reduces stall AoA mainly on thinner wing profiles.
Aeroplanes which use lift dumpers as speed brakes. Deflection of the spoiler reduces the stall AoA, a leading edge device provides extra AoA margin.

Image source and source of info below
The four main types of leading edge devices are:

LEADING-EDGE SLATS are small, highly cambered airfoils forward of the wing leading edge, which experience large suction forces per unit of area and reduce
  the suction forces on the basic airfoil.

Note that before deflection, the slat was part of the wing nose. Its area is mainly deflected to a new position, not extended as in the case of a trailing edge flap.
Slat deflection does indeed change the camber, by reducing the local AoA. This potential reduction in local lift coefficient is compensated for by the changed suction forces around the nose, with a net effect of around zero.

KRUEGER FLAPS perform in the same way as slats, but they are thinner and more suitable for installation on thin wings. Krueger flaps are often used on the inboard part of wings, in combination with outboard slats, to obtain positive longitudinal stability in the stall.

(PLAIN) LEADING-EDGE FLAPS (hinged noses) are less effective than slats. They are mechanically simple and rigid and partic- ularly suitable for thin airfoil sections.

FIXED SLOTS are the simplest devices for postponing leading edge stall, but their profile drag penalty is generally prohibitive for effective cruising, except on some low-speed STOL aircraft.

The picture below plots what happens upon deflection of flaps (left) and slats (right). Flaps increase lift for a given AoA, but reduce critical AoA. Deflection of leading edge devices does not result in increase of lift at an AoA, but postpone the critical AoA - in order to obtain more lift, the AoA needs to be increased.

Don't some leading edge devices increase wing camber and/or area? Wouldn't this lead to higher lift at a given AOA?

Yes a leading edge slat modifies wing camber - by decreasing its AoA. A trailing edge flap increases local AoA.

Ohhh that makes sense. Thanks


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What DAL level is IFE software certified at?
An inflight entertainment (IFE) system has software for the computers and for the seatback displays. What DAL level is the software classified at?

Welcome to aviation.stackexchange! You are asking many questions at a time. Could you please rephrase your question to only ask for one thing. You can then create more follow up questions and link them to this one.

Done. Thank you.

DAL is specific to a design and installation. It's a flow down from the aircraft system requirements and design and the safety assessment process.
These processes are defined in SAE ARP4754A Guidelines for Development of Civil Aircraft and Systems and ARP4761 Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.
ARP4754A is the more relevant to this question. A summary of the process is to start with a Functional Hazard Assessment which identifies hazards associated with failure modes of specific functions. Based on the severity of the failure condition a Functional DAL (FDAL) assignment is made.
The next step is to assess the architecture for functional and item independence. This allows for setting Item FDAL for each of the components of the system.
It can get complicated, but for a simple example: If you have an FDAL B and FDAL E function combined into a single item with no independence, the IDAL of both becomes Level B. If they are functionally independent and also independent items, the IDAL would match the FDAL for each.
Back to the question: An old colleague of mine worked much of the certification effort for the B777 IFE when he was at Boeing. As he explained, the highest criticality function in the IFE is the PA override function which is FDAL C. The rest of the IFE system was set at Level D. (you could argue for Level E based on the argument that losing it has no safety effect, but the Level D is based on the requirement that you show non-interference with any other system.)
The question as posed, is about the software which means we're asking about IDAL. If the IFE SW architecture is a single application or multiple applications that lack independence from the PA override code, the IDAL for the IFE SW will be Level C.
It may be possible to architect the SW with proper hardware or software partitioning to provide independence of the functions and items. In that case, the independent items could be developed at the lower IDAL level.

While I haven't worked directly with IFE software, I would expect it to be either DAL D or E, depending on the integration with the rest of the cabin systems.
Most likely it would be DAL E, as the failure of the IFE system should have no bearing on the safety of the flight systems themselves.

...unless you're on Swissair 111, but that wasn't software (I think).

From the reports, Swissair 111 was likely cause by the IFE wiring, definitely not the software.

I can answer with certainty on several products I am familiar with that they are certified to DAL C.  This seems a bit much in my personal opinion, but it is a fact.

Is that DAL then driven by the specific OEM/installer? I don't recall a TSO geared towards IFE systems to help guide their criticality level, which leaves either PMA or TC/STC.

I am not certain what drives this, it is a different division that handles these particular products.  And for clarification, the hardware is various power supplies for the IFE systems, and not the displays themselves.

Please note that we are talking ONLY about IFE software and not the IFE system. I am having a hard time visualizing why it would be at DAL C - there is nothing in there to be at a failure condition of "major"


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Is it legal to fly without a radio in Germany?
Most people in the aviation world know that it's legal to fly a Super Cub without a radio in the US. Is it legal in other parts of the world, specifically Germany?
I stumbled across this section in a copy of the German AIP VFR:

GEN 1-12 Radio and Air Navigation Equipment of Aircraft (NfL II-11/05)
...

Radio and air navigation equipment for VFR flights

(1) For VFR flights, aeroplanes, rotorcraft, powered gliders, gliders,
  aerodynamically controlled ultralight aircraft, gyrocopters, airships,
  and free balloons shall be equipped with one VHF transceiver covering
  at least those frequencies in the range 118.000 to 136.975 MHz that
  are required for the planned flight; the transmitter output power and
  receiver sensitivity shall be at least such as to ensure clear
  radio-telephony communication with the ATC and AIS units, taking into
  account the operational characteristics of the aircraft and the route
  flown.
...
(3) Para 1 does not apply to flights at aerodromes without an ATC unit
  which are conducted during the day and which do not leave the vicinity
  of the departure aerodrome (Art. 3a para 3 of the German Aviation
  Regulation [LuftVO]). Local regulations of the responsible authority
  of a Land (Art. 21a para 1 of the German Aviation Regulation [LuftVO])
  shall remain unaffected.

Does this mean cross country flight without a radio is illegal in Germany? Or is the part "shall be equipped with one VHF transceiver covering at least those frequencies ... that required for the planned flight" a loophole meaning you can go as long as you don't cross into any areas where radio is required? (thus effectively rendering 3.(3) above superfluous)
I understand that as long as you remain in class E and G airspace, I don't actually have to talk to anyone; would I still be legally required to carry a radio?
Ignore the other airspace classes for now, as C has mandatory radio communication and F has its own can-of-worms rules in Germany, and neither A or B are used at all (class F is about to be discontinued and replaced with class G and a Radio Mandatory Zone in accordance with EU regulation 923/2012 "SERA")

Where did you read that class F in Germany has mandatory radio communication? This only applies to IFR flights, not to VFR.

@SentryRaven you're right. Sorry. There's something about having mandatory radio monitoring when an "F(HX)" is not active or something. I'm not sure, I've removed that part.

Even when the F(HX) is active, you are not required to be in contact with the AFIS or ATC. F(HX) is uncontrolled airspace and does not require a clearance, as long as you are operating under VFR.
Check this: http://www.gesetze-im-internet.de/luftvo/anlage_5_75.html

@SentryRaven exactly, not when it's active, but when it's inactive you're required to monitor the frequency in case it is activated. Or something like that. Or maybe not. I'm not sure :)

No, not at all. It says "entfällt" where VFR flights are mentioned, there is no requirement for me to monitor the frequency or be in contact. F(HX) are technically only there to provide separation between IFR/IFR and to ensure that weather minima are met. If I fly around in CAVOK, I pretty much couldn't care less if the F(HX) is active or not. This is the legal theory, but not good airmanship.

@SentryRaven You are indeed correct. It only applies if you can't maintain the weather minimums for F. See here for example: http://www.dfs.de/dfs/internet/deutsch/default/newsletter_base/newsletter_vfr/vfr_newsletter_2013/vfr_nl_1_13/nfl_i_327_02.pdf

"Does this mean cross country flight without a radio is illegal in Germany?"
I fly my glider in Germany with one of the many glider clubs in the country. This is correct, you must have a radio for non-local flights, and it doesn't matter if you think you don't have to talk to anyone. You have to have it, period, and if you think you found a loophole, just wait until an inspector decides to ramp check you after a flight. It doesn't have to be a permanently installed radio -- a handheld will do. If someone can afford an aircraft in Germany that can do cross-country flights but can't afford even a handheld radio, maybe that person should consider some other hobby.

Does this apply to hang gliders and paragliders?  In the UK the radios these use (if any) are low power with a different frequency range to GA

Yes, it does. If you have a radio that does not meet the German requirements, then you can't fly cross country until you beg, borrow or buy one.

paragraph 3 clearly states that the only exception to the requirement to carry a radio set is when you're not leaving the immediate vicinity of the airfield, and then only when there's no ATC coverage.
That effectively means you can fly a few circuits at low altitude over a small field, but even then many of those would be close enough to a larger airport that has ATC coverage that they'd be covered by that airport's ATC system rather than having their own.

The only "loophole" would be if you could convince authorities that your flight wasn't planned, good luck with that.
Effectively that'd most likely mean you're having to prove to them that you went to the airfield without wanting to fly, just jumped into an aircraft, took off, and started zooming around the sky. Something that's so far out there nobody's going to buy it.

It does say the "frequencies required for the planned flight", but airspace E and G has no required radio communication, thus no required frequencies? Although you could argue that you still need a VHF transceiver, it just doesn't have to work. :)

Each flight which leaves the vicinity of the airfield as described in Art21 LuftVO is a planned flight. And with this, you need to have radio equipment installed in the range of 118.000 to 136.975 MHz.

@SentryRaven yes, I'm not contesting that the flight is planned, I'm asking about the "required frequencies" for said flight. Or is that not actually what the regulation says?

@falstro it means just that, you need a radio set capable of tuning in on any frequency you may encounter, and that includes emergency frequencies. And no, there's very little uncontrolled airspace in Europe, it's not the US. And you should know better than claiming "it just doesn't have to work". If it's on the aircraft, it should work.

That's not true, there's a bunch of uncontrolled airspace in Europe. Except for control zones, controlled airspace very rarely reach below 1000 ft AGL. And just like in the US, class E covers everything above a certain altitude, in Germany, it's 2500 ft AGL unless lowered, e.g. to 1000 ft AGL. In contrast to the US there's no surface E in Germany, the only surface airspace are D-CTR, G and F, of which the first covers a very limited space around controlled airports, and the latter two are uncontrolled. And even so, E is controlled, you are still not required to use the radio.

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text:
Do flares affect IR tracking devices?
If an IR device, such as a tracking FLIR system (not a heat-seeking missile), tracks an aircraft and that said aircraft would launch flares. Is the IR tracking device likely to be confused by the flares?
Obviously, the point of defensive flares is to decoy missiles. I want to know if other IR devices tend to be as fooled as a missile.

do you understand that those two are by design to work against each other? there are really great and crappy flares and IR trackers so it really depends on which particular instances you are talking about, e.g. first-gen AIM-9 missile vs the greatest countermeasure today or first-gen countermeasure with latest-gen AIM-9?

What makes these next-gen countermeasures superior to the old ones in fooling the missile and vice-versa? I'm assuming the answer of my question is "yes depending on the equipment used"?

yes it's pretty much like asking "is a spear likely to pierce a shield?".

Is it really a flare if it doesn't affect a tracker?  Isn't it then just a shiny, ineffective doo-dad? :)

I edited my question to be more precise on what I am asking.

I want to know if other IR devices tend to be as fooled as a missile.

No.
Modern imaging systems are not susceptible to flares in the same fashion as older missile seekers, which is precisely why modern missiles like the ASRAAM and AIM-9X use imaging seekers.
The reason flares worked at all was due to the physical layout of early missile seekers. These used a photocell detector that was sensitive across a wide field of view, on the order of 90 degrees. The trick is how do you use a device that basically provides a "yes, there is something in front of me" to track a target down to the sub-degree precision needed to actually hit it from long range?
The common solution, the "chopper", was to point the photocell forward and place it immediately behind a spinning metal disk with rectangular slices cut out of it following the pattern of slices on a pizza. As the disk rotated, the slices would periodically line up between the target and photocell, causing the photocell to give off a brief flash of power. For instance, if the target was above the missile, the photocell would see it whenever one of the slices was oriented vertically.
The frequency of the pulses was the same as the speed of the disk's rotation. These were sent into a smoother that produced a sine-wave output that peaked, in time, where the target was located. That means that the phase of this output encodes the relative angle between the missile and the target. By comparing this signal to the signal driving the disk motor, the resulting "error signal" directly encodes the direction the missile has to turn.
Early missiles were this simple, feeding the amplified output of the sensor directly into the control surfaces. The resulting flicking motions of the controls became known as "bang-bang". This was extremely inefficient, so a number of additional tricks were used.
The main one was to adjust the motion of the controls by the "angle-off", the angle measured from the missile centerline to the target (as opposed to the angle around the missile body, like a clock). Recall that the slits are rectangular. This means that the amount of time that the signal is present, it's pulse width, is dependant on how far the target is from the center of the disk.
For a target near the center, there is an almost constant signal because the linear motion of the slit is much slower (think of a record turning) and the slits are very close together. In contrast, a target near the outside instead creates very brief flashes at a single time. By subtracting the averaged signal from the raw signal you can determine the angle-off.
So here's why flares were so effective...
For simple bang-bang systems, the flight controls would suddenly start receiving more than one signal. As the aircraft flew away from the flare, the controls would begin flicking back and forth, causing it to track to the center of the two. This not only made it miss the target, but could lead it to run out of energy due to all the drag from the constantly moving controls.
In the case of the more sophisticated sensors, which includes many early missiles like the Sidewinder, flares can be even more effective. That's because when the signal from a target at the center is evened out it goes to zero, so if the missile is tracking properly it has little signal to work with. As the flare moves away, the aircraft's signal remains low but the flare's becomes huge, drawing the missile away from the aircraft. As the missile centers on the flare its signal disappears too, but hopefully after the aircraft has exited the seeker's field of view.
Both concepts only work if the flares move away from the aircraft with some speed - they are generally useless on helicopters for instance. For these types of roles, a new system was created. This normally consisted of an electrically heated block of metal or ceramic, with a series of metal shutters in front of the block. The shutters flicked open and close, producing random flashes of IR on the seeker. This caused the guidance signals to have random peaks, causing the missiles to fly around tracking the phantom signal. Another concept uses a low-power IR laser and a scanner like the ones in a supermarket to cause the beam to periodically pass by the missile, presenting a similar random pattern.
None of these systems work against imaging systems or seekers. For one, they no longer use timing to create the control signal, but instead use a variation of contrast tracking. Hot block decoys image at the same location as the target, so they simply increase the tracking signal, precisely the opposite of what you want. Flares, in theory, can still work, but even trivially simple image recognition systems can measure the size of the IR signals and immediately reject small objects like flares. And with modern processors, one can easily calculate the speed of all of the objects and look for ones that are rapidly slowing down.
Flares still have considerable utility against man-portable and older ground-launched missiles for the simple reason that most of the ones you are likely to meet in the field, including both fSoviet and US models, use some variation of a chopper. You can also release massive numbers of flares and attempt to obscure the target when the missile is far away and it cannot resolve the flares, but that can be accounted for by tracking the release points.
Against a modern missile, flares are generally useless. This has led to the concept of a towed decoy that is essentially a small plane on a wire. These can, theoretically, fool imaging seekers, but I suspect they are not as effective as one would wish. Thus the move to longer and longer-ranged missiles, where the fight really comes down to who has the best radar - which is likely always going to be "the west".
Another approach that is seeing some interest is the use of IR lasers to dazzle the seekers. These generally use UV seekers to look for rocket motors and then scan a laser around that area. If the laser hits the missile it can blind the sensor long enough to escape. I'm not sure if any such system has been deployed.

Nice answer, I was just about to post a much less detailed version. But I'd contend that that flares are still not useless: they reduce the SNR the seeker head can obtain, which increases the effectiveness of other countermeasures. As for towed decoys, they're more jammers than decoys, but are a measure against RF, not IR missiles.

Yes that's what military aircraft are doing when they dispense strings of flares during attacks as protection from heat seeking missiles.

In general, yes.  Flares burn very hot, hence emit a large flux of IR, which reads as an alternate target for any IR sensor.
Whether the decoying is successful depends a lot more on the software in the tracker (missile head, say) -- if it's like a 1970s police speed radar, and tracks the strongest signal, any old flare hotter than the jet exhaust will pull it off the intended target.  If it's programmed to ignore secondary targets once a target has been acquired, the flare has a much harder job.
There are ways to make a flare look more like the primary target, and there are more sophisticated ways to make a tracker ignore the decoy.  Like the age-old war between weapons and armor, which one is ahead at any given time depends on who made a technology breakthrough, and managed to implement/deploy it, most recently.  Just as radar chaff largely became obsolete in the 1970s, flares are obsolete in some ways (they don't bother radar tracking missiles at all, for instance, though there are other ways to decoy or lose those) -- and still vital in others.
Other IR systems, like FLIR, will surely detect and display the flare as an IR source, likely a brighter one than the aircraft's engine -- but since FLIR is a human-interface display technology, rather than an automatic system, whether it is "distracted" is up to the operator.  A skilled FLIR operator is very unlikely to lose the primary target due to flare launch, unless a flare does a very good job of emulating the temperature and heat flux of the engine, and the engine significantly changes its signature simultaneous with the flare launch.


text:
Can you identify this aircraft photographed during solar eclipse 8/21/2017?
The following sequence of shots was taken about 9.5 minutes before the start of the eclipse, 1:12pm EST.
Shooting in burst mode off of a tripod - all 3 shots taken within 1 second. Burst mode is 14 frames per second, so it's reasonable to assume that these 3 photos were taken 1/14sec apart.
Exif:
Camera: Canon EOS1DX
Lens: Sigma 150-600mm Contemporary.
1/8000s, f/29, ISO 100, focal length 600mm. No filter.

First image: the aircraft is seen above the sun - no contrails.
Second image: completely different trajectory and a contrail (?)
3rd image: the aircraft is gone.

Zoomed in:

About the trajectory: the wind is probably moving left to right.

The contrails in the second image are missing in the first. Contrails can't appear behind an aircraft retroactively like that. In the second image they are right up against the aircraft. These images likely do not show the same aircraft.

Where in the US was that photographed?

Perhaps if you can give exact time and location FlightRadar24 could be used to identify the aircraft.

If I've measured the pixels correctly, this object travelled about 26 times its own length between the two frames.  If the frames are only 1/14 of a second apart, this is bloody fast;  for comparison, an SR-71 blackbird travels about 2.2 times its body length in the same amount of time (assuming a speed of 2200 mph.)  Hell, the Space Shuttle "only" travelled about 10 times its own length during re-entry.  Either the time between the frames is much different than 1/14 second, or this isn't an aircraft.

(the Space Shuttle "only" travelled about 10 times its own length in 1/14 second during re-entry)

@gamecatcher Were these three the only ones taken in the one second, or were there fourteen? the fewer frames that are taken, the longer the intervals should be. that would effect the speed calculations hugely.

Even with 1 second between every shot, the contrail of that length wouldn't appear and then vanish in one second - let alone 1/14 of a second. This has every indication of being a complete waste of everyone's time & attention, either a technical glitch in the camera or a hoax.  (NO FILTER??? And the camera wasn't fried? Bet there was SOME filter involved!)  And in every case, entirely off-topic at Av.SE. This thread needs to be moved to skeptics.se or deleted in its entirety!

No filter?  How did you not fry the sensor in that camera shooting straight at the sun?

Why was the "military" tag applied to this thread?  Doesn't that pre-suppose that the answer to the question has to be a military aircraft?

Why was no location for the photos mentioned in the post?  Wouldn't a person seeking answers want to provide that sort of information in order to help those who'd be interested in answering?

@Notts90 It looks delta-winged, which would make it military. Military planes usually aren't on tracking websites.

Based on the second picture and the list of US military jet, I would guess F-22 Raptor, and since this kind of aircraft usually fly by 2, the jet in the first picture is maybe a second F-22.

As for the timing of the shots, the trail we see in the second pic not appearing in the 3rd is telling me they were shot with at least a couple of seconds interval. That would also explain why each jet appears only in one pic.

" is telling me they were shot with at least a couple of seconds interval" but the timestamp is the same for each photo, suggesting, as the OP said in the question, that they were shot within a much smalle timeframe

The first plane that came into my head after seeing these pictures was the F-117 Nighthawk:

However, this object pictured could easily be something else (maybe not even a plane) due to the low quality of the object and its speed, so no answer will be 100% accurate.

I was under the impression the Nighthawk fleet had been retired years ago. Are there any still flying?

Yes I was thinking the same whilst I was writing the answer. However they may still have a few left over. But I have no idea if they would fly them.

Nvm I found this website explaining why we might still see them in the skies. http://intercepts.defensenews.com/2014/11/we-now-know-why-the-f-117-is-still-flying/

@Mark That article is from 2014. Plus, the shape of the image doesn't have two distinct wing tips, but instead has a singular surface, more like that of the X-32, but even then, it's not similar enough. I doubt it's either one. https://s-media-cache-ak0.pinimg.com/736x/0e/2d/a7/0e2da7402ec1f2275de092cd66af47c0--youth-fighter-jets.jpg That, plus the contrails suddenly appearing where they were not in earlier images, makes this collage seem very fake.

At the level of detail shown in the photographs, it could be pretty much any delta-winged aircraft. It seems much more likely to be something in current inventory.

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text:
What's an ESAT as filmed in "Top Gun: Maverick"
This is an image from the movie Top Gun: Maverick
The scene in question is between 01:48:20 - 01:48:34
In the movie they're calling this device an ESAT, which is sending some signal which is visible on their radar
Now, I don't see any marker on this device which is telling me that this is pointing to "GPS", which most probably is a GPS transmitter for communicating their location, not GPS receiver
And the other options are "VOICE", "406 BCN", and "TRIPLE BCN"
From these options, I understand this is some sort of device for communication based on different situations
What is this device called generally ? Something that I can Google and read about because I don't see anything named ESAT on Google.
And, what are those other 2 BCN options ? Can't find anything about them either on Google.

ESAT probably have something to do with SARSAT and Satellite Aided Tracking. This dial is typical of the AN/PRC series survival ratios. Military pilots carry those on every flight so eventually someone would identify this one. (Maybe this is PRC-125 but I can not find any pictures of it).

If you google the AN/PRC-90 you’ll get very close.  I am guessing this is either (a) a more modernized replacement, or (b) more likely, a “dramatized version” of the PRC-90 with dramatized features.
As for double/triple beacons… There are actually 3 frequencies set aside specifically for emergency, ELT, and EPIRB applications:  121.5 MHz, 243 MHz, and 406 MHz.  (Hence the “406 BCN” label on the knob.)  A device could transmit a “civilian intended” beacon on 121.5, a “military intended” beacon on 243, or a GPS location encoded beacon on 406.
I was an Army officer in special operations many years ago and the appearance, features, and functionality of almost everything we carried ended up quite dramatized for movies.

Hollywood makes stuff up? I'm shocked! Thank you for your service.


text:
Can a GPS signal sent to a plane be spoofed?
Related to What effect would an air-to-air GPS jamming system have?, I'm wondering whether it is possible for a terrorist (or likewise, law enforcement) to manipulate GPS signals received by a jet, re-routing it elsewhere?
I gather this would be far from a simple task, but how feasible is it?
Let's assume that this is in uncontrolled airspace, so atc can't spot the change in flight path.

it's possible but the pilot would need to ignore every other navigation aid he has available

Spoofing GPS means broadcasting a false GPS signal - This is harder than jamming GPS which can be done relatively easily by broadcasting a strong random signal at the relevent carrier frequencies.
GPS receivers use GPS ephemeris tables which tell them where exactly they should expect each satellite to be. So the false GPS signal has to look enough like a real GPS signal that the receiver will accept it and use it's transmitted data in it's calculations.
Of course, if, for example, the expansionist president of a country with advanced avionics capability decided to supply sophisticated equipment and the associated personnel to a separatist group in a neighbouring country, it might be possible for them to bring about this kind of result.
There have been reports of this kind of spoofing actually happening, so it appears to be possible.

The U of Texas students built a GPS spoofing device for about $3,000. A pair of students, the “attackers,” then sat aboard the upper deck of the White Rose, where their GPS spoofer emitted a counterfeit signal slightly stronger than the real GPS signal.

This was a yacht at sea, presumably out of sight of land on a featureless ocean.
It may be more difficult to achieve this with an airliner, which have a variety of navigational instruments, including radio navigation beacon receivers. Inconsistent indications may alert the pilot to a problem.
Non-GPS navigational instruments/systems that may be found in an aircraft include:

VOR
DME
NDB/ADF
TACAN-DME
ADIRU

The loss of an RQ-170 in December 2011 involved GPS spoofing; see this Wikipedia link, although none of this has been confirmed. GPS jamming is so dead simple that all aviation navigation requires alternatives which do not rely on GPS. However, GPS is so convenient that in many cases it is used as the primary means of navigation.

It would be interested to know to what extent the modern navigation systems cross-reference GPS with INS. INS is always there because GPS alone has too slow response for some uses like autopilot and being completely internal INS obviously can't be spoofed, so when the systems divert more than is believable error rate of INS, the system can declare error. What I don't know is what the threshold for declaring the system failed is in practice.

Yes, you could certainly do this, especially for a smaller plane like a charter that was flying an unknown route. By this means you could temporarily divert the aircraft. Note several things:

You would have to do it gradually; if you made a sudden change in position, the pilots would probably notice, so it would only work on a long flight

It would not work if the pilots knew the route well. What would happen is that the trick would start to influence the heading and the pilot would see the unexpected heading and get confused (why are we on 040? shouldn't we be on 052 to Chicago?)

The diverted heading would have to be roughly similar to the expected heading. For example, if the pilots know they are going north, and the diverted heading is south, they will immediately know something is wrong.

If it was a domestic commercial flight or at least had a flight plan with flight following activated, it would probably get noticed by ATC. For example, even a private pilot, if he has requested flight following will get notified by ATC if he starts to deviate significantly from the planned route. For this reason, a diversion would be most effective if it was an international flight or going through uncontrolled air space.

As far as the spoofing itself, it is easy as long as the person has enough expertise. Even a weak earth-bound transmitter will easily overpower real GPS signals. To create the spoofed signals the engineer can use a GPS simulator on the planned diverted route and record them. Then, they just play back the simulation record and transmit it. Note that this will only work if you know ahead of time the aircraft's planned route and speed. If you do not know ahead of time its original trajectory, you would have to observe its current flight path (by ACARS, radar or some other method), compute the diversion, simulate it and transmit it dynamically, which would be more complicated.
Also, don't forget that EVERY GPS receiver in the area of effect will receive the spoofed signal, so if it is broadcast in a populated area, you will have thousands of cars, phones and boats all receiving the spoofed signal.

cool idea to play back pre-recorded GPS signals. Unfortunately the clock time is a very important parameter in GPS, and the systems (and pilots) would probably notice that changing.

@Peter I assume the spoofer knows the original flight plan so can make the GPS time relatively similar to the real time.

authors: Юрій Бондаренко


text:
Are experimental aircraft exempted from the 2 year transponder and avionics checks?
Are experimental aircraft exempted from the 2 year verification test for avionics, transponder and altitude encoder? Or must they comply?

Which legislation?

What's BL?  Are you asking about the regulations under FAR 91.411 and 91.413?

When you operate in airspace that is under FAA regulations, FAR 91 applies (unless you are flying military)
FAR 91.413 a) states:

(a) No persons may use an ATC transponder that is specified in
  91.215(a), 121.345(c), or §135.143(c) of this chapter unless, within the preceding 24 calendar months, the ATC transponder has been tested
  and inspected and found to comply with appendix F of part 43 of this
  chapter;

So when you haven't performed the two year transponder check, you are not allowed to use the transponder. The way to fly then is to fly VFR in airspace where no transponder is required AND not to use the transponder at all.
This is not specific to experimental aircraft, there is no exemption.
There is good reason not to have an exemption for experimental aircraft; a malfunctioning transponder can cause many problems to the ATC radar systems.

If you have a transponder installed, it must be turned on (except in Class G airspace) §91.215 (c) Transponder-on operation. While in the airspace as specified in paragraph (b) of this section or in all controlled airspace, each person operating an aircraft equipped with an operable ATC transponder maintained in accordance with §91.413 of this part shall operate the transponder, including Mode C equipment if installed, and shall reply on the appropriate code or as assigned by ATC.

@JScarry According to §91.215(c) the transponder must be turned on if it is maintained in accordance with §91.413. The case that is being discussed here is when the transponder is not maintained in accordance with §91.413.

You stated that if you fly in airspace where it is not required then you can turn it off. That is not true. If you have a transponder, it must be maintained and turned on. You can’t fly in controlled airspace with it turned off or not maintained. An interesting loophole is that if it was inspected and subsequently fails, you can turn it off and fly in controlled airspace.


text:
What percentage of airliners today operate with unaugmented GPS equipment?
Responding to this question there was some discussion on GPS equipment and whether it used augmentation (WAAS/SBAS/GBAS) or not. What percentage of airliners operate with unaugmented GPS equipment? Maybe restrict to US/Europe to simplify. It might be easier to identify certain sets of airliners which have augmented GPS, which I would consider responsive.
I found the FAA first authorized use of WAAS for instrument approaches in 2003, which was also when the first WAAS approaches were published.

A SBAS delivers corrections and satellite integrity data, but only for a region, and only for some constellations. WAAS is the SBAS providing GPS augmentation over the North America region. Another SBAS must be used when operating with GPS in another region (e.g. EGNOS when operating in Europe) or when using another constellation (e.g. EGNOS provides augmentation over Europe both for GPS and Galileo).

In the US, this is rapidly in flux. There's an effective FAA ADS-B Out requirement for SBAS or multi-frequency/multi-constellation. It was supposed to take effect January 1, 2020, but there's exemptions out to December 31, 2024. After that date, it should be pretty close to "none".

Both sources you linked say "WAAS is not required", you just need "adequate accuracy (within 0.05 NM)". Do you have a source that actually shows most airliners in US airspace have an SBAS receiver installed?

@Bianfable You misunderstand. Read the first link again. It says WAAS is not explicitly required but it is the only technology at this time that meets the requirements. Any other receivers, like GPS L5 and GPS+Galileo would include WAAS anyway.

I read that sentence as: with WAAS you meet these requirements >99.9% of the time, without WAAS you might meet these requirements at less than 99.9% of the time, but are allowed to fly. So an aircraft without WAAS would be allowed to operate as long as uncorrected GPS is currently accurate enough.

@Bianfable Nope. Read the next paragraph. What WAAS is needed for is integrity data. With unaided GPS, there is no guarantee that 99.9% of the time your transmitted position is correct due to the risk of a GPS fault. Obviously, failures cannot be predicted ahead of time. "An aircraft that is not equipped to meet the requirements of this rule will not have access to the airspace for which ADS-B is required."

@Bianfable Other sources: Textron "ADS-B will require at least one Wide Area Augmentation System (WAAS)-capable GPS receiver connected directly to the transponders." AOPA "Two things are required for ADS-B Out capability: an approved position source—generally a Wide Area Augmentation System (WAAS)-approved GPS receiver—and an ADS-B transceiver."


text:
Why has Pakistan bought J10C?

Pakistan inducts China-made J-10C fighter jets into PAF

According to the above article, the purchase of J10C was the response to India's purchase of Dassault Rafale.
Can anyone please explain why or how?
What were the factors that could have been motivated Pakistan's purchase of J10C aircraft from China to tackle Indian Rafales?

A main concern here is the radar and electronics. Radar on the JF-17 isn't the best due to its size limits, while the Russian radar on Su-30MKI isn't great, either. Both sides want to acquire fighters with ESA radars to gain advantage over the other.

What were the factors that motivated Pakistan's purchase of J10C aircraft from China to tackle Indian Rafales?

I've no insight into the motivations of Pakistan's senior officers but I imagine the following factors were important

Multi-Role Combat Aircraft primarily intended for Air to Air operations.
Similar max airspeed to Rafale.
Better ceiling than Rafale.
Ability to carry short and medium range air-to-air missiles.
Cheap (1/4 the price of the Rafale)

cheap? or less expensive? :)

While some of the price difference might be because manufacturing in China is cheaper, I suppose most of it is actually the bells and whistles in the radome and avionics bay. Which makes a huge difference—these days fighters rarely get into manoeuvring combat for the raw performance to make a difference, usually they just fire missiles at each other at long range and then the biggest advantages are better radar, tracking software and countermeasures. And good AWACS downlink.

Maybe they finally found a market for their old planes. Perhaps in Ukrainia.

The point about multirole aircraft: weren't the F-16 already multirole?


text:
Do you know the exact model and use of this rotorcraft?

I've tried to identify this. Someone suggested it is a Bell 206, possibly a Jet or Long Ranger. I disagree.
I think it is a US Coast Guard helicopter. It flew over my house in Mobile, Alabama. It's been difficult identifying from this angle I photographed it.

Could you please explain why you do not think it is a Bell 206?

Because the photo that  I've seen of a Bell 206 didn't match up with this one. If you look at the nose you will see the glass above and below center piece dividing them. You can see the blade on the left thru the top glass.. While I realize there are variations of the Bell 206 (Example-TS 57 Sea Ranger) , I'm still not sold until someone finds this particular plane.

I'm not versed in military markings, but do the star/bars symbol underneath denote it is not a civilian aircraft?

Also, you saw it in straight and level flight, so can you check a map and backplot the path?  That may give you an idea of where it was coming from and going to, which could give you somewhere to make inquiries.

Criggie- according to a photo friend of mine, it has a US Airforce star on the bottom. I haven't varified that as of yet. I believe it was getting ready to land or just took off from a local airport about a mile or two away-Mobile Reginal Airport. I wil check and see if this airport has this type of plane coming and going. Since checking into this I got a Google message pop down on my computer asking if they can have my location. I hope I didn't set off red flags somehow. I'm a photographer and I photograph everything. Especially, planes etc passing over my house.

It's a Bell TH-57, most likely a TH-57C, which is the Navy's variant of the Bell 206 JetRanger.  It's used for VFR and IFR helicopter primary flight training for the Navy and Marine Corps.  Most likely that picture you took was of a TH-57 out of Pensacola NAS on a training flight.  They like to come out to KBFM and Jack Edwards in Gulf Shores to practice flying, pattern work, etc.

Carlo -the glass on mine apprears to meet with the center line that divides both top and bottom glass. You can see the blade in the upper left corner. I'm not saying there isn't a variation to the Bell 206 that matches. I just don't believe the TS 57 Sea Ranger is the one that does.

Carlo, I appreciate your help. It was flying low enough to believe it had just taken off or getting ready to land. We have Mobile Regional Airport about a 1-2 miles from my house.

If by glass you mean the forward windshield meeting with the lower transparencies, it doesn't; it's just from than angle, it's difficult to discern the nose of the aircraft from that angle; and the nose glare shield will appear to look like glass from than angle in the sun as well.  You will often see TH-57s parked out there at KBFM at Signature Flight Service near the Airbus hangars.

Your very first statement above your photo states as follows-
It's a Bell TH-57, most likely a TH-57C, which is the Navy's variant of the Bell 206 JetRanger. It's used for VFR and IFR helicopter primary flight training for the Navy and Marine Corps

...........and??????

YOU DIDN'T look close enough at my photo. The stars and stripes insignia on the undercarriage stand for US AIRFORCE. might want to check for a rotocraft that has glass above meeting with a divider of the glass below , under that branch of service.

The US roundel - which is what I'm guessing you mean by 'stars and stripes' - on the belly of the helicopter is common to all US government and military aircraft.  The Army, Navy, Air Force, Marines and Coast Guard all display that roundel on their aircraft.  As for the 'glass', you didn't read my previous comments about the perspective and lighting effects.

The TH-57s used to be based out of NAS Whiting Field, unless they have moved...

On this page is a photo of a fixed-wing craft clearly bearing the same roundel (on the underside of the starboard wing, and on the tail) and very plainly marked as a USCG asset. So, it's not uniquely an Air Force marking.

@CCTO it's been standardised for all US military (and the USCG is part of the military) aviation assets for decades, 1950s I think. Only difference is the size, sometimes the colouring (grey scale vs full colour), and that at times the entire thing was surrounded by a thin white border which has since been dropped.


text:
How practical is mid-air cargo transfer?
Mid-air refueling is now commonplace and I have even heard that passenger transfer in mid-air has been possible for stunts. What is the practicality of mid-air cargo transfer?

Related: https://en.wikipedia.org/wiki/Mid-air_retrieval

The same practicality of transferring 'packages' from makeshift submarines onto boats with four 250hp outboards on them.

You could quote an excerpt from Quora that you find particularly relevant

Certainly using a long tube to transfer cargo would be insane, and as others have said it's generally impractical. But, let's assume that for some reason it really needs to be done, and the importance of this outweighs the complications and inefficiencies.
Transferring fuel from one plane to another is already possible. Flight control surfaces are installed on the nozzle to allow an operator to accurately control its position relative to the receiving plane. Why don't we learn from that?

Scenario 1:
Transfer of cargo by zip line: The receiving plane is equipped with loading doors on the top. A zip line emerges from the back of the first plane, and is steered using control surfaces down into the cargo bay of the receiving plane. When it arrives, an operator attaches it to a fixture so that it's secure.
Next, cargo boxes are sent to slide down the zip line, using some device to slow their motion. The operators in the receiving plane receive them detach them from the line, and pack them onto the cargo hold.
Scenario 2:
Transfer of cargo by aerodynamic body: What if the cargo could be 'flown' from one plane to the next? The cargo is packed into an aerodynamic container which emerges from the back of the first plane, attached by three tethers.

The cargo can be steered by controlling the lengths of these three tethers. This gives 3 degrees of freedom in the control, allowing the cargo to be steered relative to the second plane, which is following the first plane at a slightly lower altitude. Again there are cargo doors on the top of the plane to accept the cargo. Alternatively, the cargo simply attaches to the top of the receiving plane, like the space shuttle.

The cargo is Hatsune Miku?

It's technically feasible to do this, there are mid-air capture systems already, developed to snag payloads returning from space (film, samples, etc) which are descending by parachute. There are fixed wing and helicopter versions of the technology. So, you could drop a cargo out of the back of one airplane, and another could catch it, winch it in and fly it somewhere else. In fact, technically this has been done numerous time as the testing of these systems and training of the pilots involved pushing the test article out of the back of another airplane.
The reasons it's impractical to use this are:

It's expensive: The hardware costs money and adds weight to the aircraft, the aircraft have to be unpressurized if the cargo is to be winched in, which some cargo won't tolerate, the aircraft will have much less capacity due to the equipment involved, and other reasons
It's dangerous: Flying an aircraft into a parachute or other drop system is inherently hazardous, it's only done when there's no other alternative
It's weather intolerant: whatever solution is used, the transfer would need decent weather conditions, and probably need to be done during the day, which would limit it's utility
It has no practical benefit: transferring cargo from one perfectly good airplane to another one doesn't get the cargo there faster, safer, or cheaper. If the cargo needs to go where an airplane can't land then it can be transferred to another one, or to a helicopter at a field. If time is of the essence then the cargo can be air-dropped. There's no problem that mid-air cargo transfer solves

Footnote: Air drops can already use steerable parachute systems.  Air-launched UAVs would provide the manoeuvrability of a small aircraft after transferring from a  large, fast, long-range aircraft, but without the transfer, if there was a need for greater range or precision away from the parent aircraft

"the aircraft have to be unpressurized if the cargo is to be winched in, which some cargo won't tolerate"
If the cargo can't handle the unpressurized aircraft, then it probably would already be damaged before it gets winched in. Considering where it came from :)

@ChrisH the air-launched UAVs already exist too, e.g. the Silent Arrow GD-2000

@ErinAnne I thought read something about it, but couldn't track it down again having forgotten the name

+1 for the last sentence.

air dropped... the original "drop shipping" (hehe)

"There's no problem that mid-air cargo transfer solves" except of course saving President Harrison Ford.
https://www.youtube.com/watch?v=3Unwbu-dhYM

"doesn't get the cargo there faster, safer, or cheaper" - but it does get there. And if coca doesn't grow well in your climate....

This honestly sounds like something that would only be practical in the craziest of emergencies, like the President Harrison reference @Ryan_L made or if you were reacting to a crazy dynamic battlefield scenario where you had two planes in range and only one of them had any bombs left and you needed to hit two targets simultaneously, and immediately. Would make for good fiction, at any rate.

"transferring cargo from one perfectly good airplane to another one doesn't get the cargo there faster, safer, or cheaper" - Unless the first aircraft is low on fuel, and the second one full.  Midair refueling would be better, but maybe the first aircraft is incapable of that for whatever reason.

If the first plane is low on fuel it needs to land @aroth, not loiter while cargo is transferred.

"Low" in this context ought to be interpreted as "not enough fuel to fly the cargo directly to its final destination, but enough to effect a successful mid-air transfer to a second plane that can reach the final destination".  I'll grant that it's risky and expensive, but as long as the transfer isn't unreasonably slow it should get the cargo there faster than landing, refueling, and taking off again.

Grossly impractical, and manifestly unsafe as well. Here are a few reasons why.
To transfer cargo from one plane to another requires mechanized material handling systems which can be extended hundreds of feet through the air from one plane to the other and retracted again when the job is done, while the plane is flying at perhaps 200MPH or more. Every pound of material handling machinery built into a plane represents a pound of lost payload, in a business where a fuel cost increase of order ~pennies per pound is enough to ground an entire fleet of cargo planes.
Now imagine the size of the cargo conduit itself. It will have to pass objects the size of a preloaded cargo bin, perhaps 6 feet on a side, so the conduit will be about 8 feet across and let's say 100 feet long.
That tube will be extending through the slipstream of one plane and into the oncoming flow field of the other plane at very high Reynolds numbers; the flow fields surrounding both planes will be significantly upset by the presence of that tube and that disturbance will grow from nothing to its full extent as the tube gets extended on a timescale of ~100 seconds.
Both planes need to be fully controllable before, during, and after the transfer process which will involve the exchange of one plane's full useful cargo load to the other, leaving one empty plane at max gross and one plane at max gross empty.
And during that process, the two planes will be physically connected together and flying at the same speed, which will require both of them to be actively trimming and modulating their power settings the whole time.
And the whole shebang must be resistant to perturbations from the environment.
...and for what purpose, exactly?

In my head there's a fleet of drones taking off from all over the UK carrying small amounts of cargo up to a 'mother-ship' that crosses an ocean (perhaps the Atlantic), then drops the drones on the other side, to deposit their cargo.

@Richard Why not just load the mothership on the ground, with cargo arriving at the sorting facility via trucks & smaller aircraft, like the way FedEx moves packages around? Take as long as you need to (within reason) to load the cargo, not burning fuel waiting for the last package to arrive.

@RalphJ - Think of the mothership as a conveyor belt. You'd have multiples of these things in continuous motion. The drone wouldn't need to travel to a central location. It would just join the mothership as it moves overhead

Cocaine is a helluva drug.

Richard's idea might get practical with a nuclear powered large aircraft, but this comments thread is becoming like WordlbuildingSE.

It's probably not what you mean, but this could be practical when one craft is so large (and slow) it can wholly contain another, such as a cargo or "aircraft carrier" rigid airship.
However, these crafts themselves are considered to be impractical (CargoLifter, DARPA Walrus/HULA), I believe largely due to the impracticality of acquiring and maintaining storage of helium (which is hugely safer than hydrogen, but still sneaks out of everything because it's so small)

While mid-air cargo transfer is technically feasible, its practicality is limited in most cargo transportation scenarios. The complexities of coordinating multiple aircraft, ensuring safe cargo attachment and detachment, and maintaining stability during the transfer make it challenging. Additionally, the cost-effectiveness and efficiency of mid-air cargo transfer compared to ground-based methods raise concerns. Although it may have niche applications, mid-air cargo transfer is not widely employed in real-world cargo logistics operations.


text:
What kind of injury would force a Navy EA-6B pilot to stop flying and take a desk job?
Currently, I'm writing up a character bio for a game, where the character is a former naval aviator who becomes a JAG Corps lawyer who can be quite active during investigations and combat.
I've been googling for an hour and I've yet been able to find any articles on this, other than a number of health conditions barring applications to the service. Can anybody suggest something with a reference?
I had been thinking that he might have some kind of eye condition or even lost a finger or two in an accident, but I can't find any cases or regulations to back these ideas up.

related: Why are pilots deemed unfit to fly after emergency ejection?

Maybe asking for navy medical requirements for flight crew would be more on-topic. If one of those is no longer fulfilled after an accident, that might justify revoking the pilot's certificate (or whatever the Navy calls it).

@Bianfable … and then cross-reference with the list of things that would get them a medical discharge from the Navy, to see what lies between.

The F-16N is used as an aggressor aircraft at Top Gun; "N" = Navy. So if the character's background were to be a Top Gun instructor, that's actually plausible. Otherwise, his background would be F/A-18's. Which the Top Gun instructor would probably have flown first anyway. (Maybe an exchange tour to the USAF could be in F-16's... tho again, having flown Hornets first.)

A missile to the knee

@RalphJ Then the question needs to be edited to read "F-16N" not "F-16C" at the least.

P.S.  You might want to look into copyright issues because this was the basis of a TV show in the 1990s.  In case you don't remember...

It does sound a bit like JAG the TV show - "After an accident during a night landing on an aircraft carrier, in which his RIO (Radar Intercept Officer) dies, it is revealed Harm suffers from night blindness, he recovered on his grandmother's farm in Pennsylvania, before returning to naval service. After graduating from law school at Georgetown University Law Center and passing his bar exam, he transferred to the Judge Advocate General's Corps."

Not that it is a bad thing to write a book like JAG the TV show!

@trognanders I had the same "DejaVu". Of course not a bad thing, but the OP should be concerned about copyright infringements if the character turns out to be too much like "Harm" from JAG TV series, since this will be part of a published game, I guess. From the little he says, the character is quite the same: "can be quite active during investigations and combat" is really "Harm"!

Both the USMC and the USN have retired the EA-6B.  If the story is to be actual, better use the F/A-18 instead?

Or to be closer to the EA-6B, maybe the EA-18G Growler would be a good choice?

Years ago I met a guy with an aerospace supplier I used to deal with in the US, who was a former instructor in the USN in the T-45 Goshawk.  I asked him why he quit flying to do what he was doing, and he told me he was in an incident where his student rolled into a turn and pulled high G to avoid something, without any warning, while the instructor was looking down at something in the back seat.  He wasn't able to raise his head in time and the G load tore ligaments in his neck.  When he recovered, the Navy wouldn't let him return to flying status so he retired.
Here is a link to a related study on ResearchGate site.
I knew another guy with another supplier who was an ex F-14 driver in the late 70s and who retired after a crash where he ejected after an engine failure at a critical point during a carrier landing go-around, while the machine was rolling on its side.  The airplane having banked quite steeply by the time the seat fired, the seat sent him on a kind of lateral arc like he'd been launched from a catapult, and he hit the water before his parachute had fully slowed him down, and broke his back, recovered (more or less) and retired.

Plenty of guys suffered injuries in an ejection that put them at a point where "the next ejection might kill you" but after rehab, they are 100% as far as you could tell - active & fit. Some continue to fly in non-ejection-seat aircraft (E-2, C-2, T-44, C-40, etc) but going JAG instead sounds plausible.

@ReverendSpeed I took the liberty of adding a link to a related study to this answer, as I'd rather not make another one similar to this one. Check it out.

That incident sounds very familiar; what year was it?

The guy I met told me he tried to transfer to the Air Force from the Navy but they wouldn't take him for flying duty either.  The story was told to me about 15 years ago and I believe happened in the mid 90s.

Glaucoma would do it -- reduces peripheral vision almost immediately (that's often the cause for diagnosis, unless someone is having medical eye exams on the regular like a diabetic would), leads to blindness over time -- but until then, has little effect on central vision (such as you'd use to examine details, shoot, etc.).  There are treatments (one of which is marijuana, which would be a big no-no for a pilot, but might be okay for a desk job with a prescription), but there's no cure.

Looking it up, there's pretty strict limits on how bad a pilot's vision is allowed to be, though it seems like the requirement of 20/20 vision was relaxed in the 90s. Anything that caused vision to degrade past the level required would be sufficient to get a pilot grounded while still live a normal life.

@nick012000, 20/20 has always been a pretty hard requirement, what varies is whether or not it can be corrected to 20/20.  Generally they want to take in pilots that have 20/20 (or better) uncorrected, but if they are short you may get a waiver.  Once they have invested a million $ into your training it would be foolish to boot you out just because you need glasses.  But again, it needs to be correctable to an acceptable level.

A bit more exotic incident would be the one that happened to Finnish Air Force test pilots about ten years ago:
During a test flight of a "frankenplane" put together of two carcasses of F/A-18's (FAF HN-413 damaged in a previous midair collision and a Canadian front section) to make a functioning F/A-18D (HN-468), a horizontal tail servocylinder valve malfunctioned while recovering from an intentional tailslide. This led to an uncontrolled dive, during which the speed of the aircraft quickly accelerated. At a speed of about 470 kts the pilots ejected, and  the plane shortly impacted ground, completely pulverizing it.
Because of the high speed both pilots were seriously injured, and to my knowledge, at least one was not able to resume flying duty.
Oddly enough, the frankenplane experiment in itself was successfull, as it was later determined the valve failure was an isolated incident, not related to the repairs made to the plane.
Finnish broadcasting agency YLE reported the incident in many news articles, here is one of them. Unfortunately it is in Finnish, but Google Translate seems to do a decent job on it.

Anything health related could be a reason. Pilots go to for checkups at the doctor at regular intervals.
Even the suspicion of a minor heart problem could be one reason. This includes ECG and other tests, the kind of small murmurs we all have has limits as they might be due to leaking valves. Training hard while having lower chest infection (severe cold) could lead to heart damage.
Gallstones or Kidney stones will stop a fighter pilot from flying. Either can be caused by reasons outside the individuals control (ie, certain diets will increase the risk, but if you stay away from those the stones can occur anyway).
Other reasons:
The type of plane you are flying might be phased out, and you are not among the pilots trained for the new type. Perhaps given the offer of "going down" to less interesting plane types and simply staying out.
Pilots go through recurring training and tests. If you are "not up to the high standards", you will not be allowed to continue flying fighter planes.
You get married and want to be close to your family -- fighter pilots move around a lot between different assignments.

Definite +1 on cardiac issues -- IRL I see a fair number of pilots undergoing cardiac MRI to comprehensively rule out nasty cardiac pathologies. One of the standard tests performed is a 'stress perfusion test' -- we inject a drug to make the heart beat faster and quantitatively see if the blood flow can "keep up" [a good sign] or if any ischaemia due to pathology (e.g. atherosclerosis) is limiting [a bad sign]. Most people sweat, get visibly stressed, etc as their heart rate shoots to ~160, which is clinically useful information. Airline pilots are oft-maligned as they just sit there calmly...

A friendly game of flag football ended a flying career - landed on head, compressed two discs, couldn’t wear a flight helmet longer than 30 minutes…

Gallstones would prolly make the most surprising character bio item.

Are you aware of the TV Series that ran from 1995-2005 called "JAG," which is almost exactly the same as your premise? It was explained in the show opening that:

Following in his father's footsteps as a Naval aviator, Lieutenant
Commander Harmon Rabb Jr. suffered a crash while landing his Tomcat on
a storm-tossed carrier at sea. Diagnosed with night blindness, Harm
transferred to the Navy's Judge Advocate General Corps, which
investigates, defends and prosecutes the law of the sea. There, with
fellow JAG lawyer Major Sarah MacKenzie, he now fights in and out of
the courtroom with the same daring and tenacity that made him a top
gun in the air.

https://en.wikipedia.org/wiki/JAG_(TV_series)
By the way, I think it was in season 3 that he had laser surgery that cured his night blindness, and he got to fly Tomcats again. He deployed to Kosovo and won a DFC, but that only lasted a few episodes. He went back to JAG after that, but he kept his flight status current.

While this is a very valid point, A) it is NOT an answer, and B) it was mentioned in the comments on the OP 10 hours ago

"Night blindness" mentioned here actually does answer the original question.

@FreeMan A) I think it does answer the question. B) Answers in comments are not allowed, so posting this as an answer with a source (even if it's only Wikipedia) is the correct way.

I bet night blindness would have been caught in the initial testing before the multi million dollar flight training...

@Jpe61 the pilot may have developed night blindness due to dietary deficiencies ... you are sure you can see at night, you are convinced you can see at night but it requires only a bit more attention because of "getting old" ...  until the time you do not see at night.

To that I would say military pilots take their duty very seriously, this would include keeping the diet healthy. But I must admit in some rate circumstances one might develop night blindness due to, say, inflamation or such. Being born with it, "you shall not pass" initial testing

Naval aviator Alan Shepard was grounded for at least 6 years due to Ménière's disease.

It may be the usual cover-up of major neglicence, such as in the ominous "accident" of Cermis, when the crew of an EA-6B flew too low, cut the cables of a cable car and brought the lives of 20 people to an abrupt halt.
https://en.wikipedia.org/wiki/1998_Cavalese_cable_car_crash
If your fictious pilot would have not had any recorder on-board, he would be actively on-duty. I think they could easily fake-up a medical report claiming he had a sudden epileptic seizure that brought him too low. The lingering epilepsy is the kind of "injury" that would remove a pilot from active line, but that can be retained in the army with a desk job.

That pilot got cleared of the manslaughter&co accusations, he clearly did not do anything wrong.
Unfortunately for him, that same pilot got dismissed for obstruction of justice: he had an onboard video recorder and he deleted the cassette, so that is the farcical reason for which he was dismissed. Life is really unfair sometimes ...

I guess it was farcical and unfair if you believe that military officers shouldn't be dismissed for "conduct unbecoming an officer and gentleman".

@DavidAldridge I am ironic (and sad). One cannot be a gentleman and reckless.

Generally, once a person is qualified as a military pilot the service will work pretty hard to bring him back to flying duty after an injury, as it's a rather large investment at that point, except that the "needs of the service" vary over time mostly based on the manning and budget set by Congress.  Your character could move to the JAG Corps for as simple a reason as already having a law degree (maybe decided to join the Navy after some life changing event made him long to serve), getting accepted to both fly and lawyer (I knew doctors who did both duties), and choosing to do the legal thing full time when manning allotment got politically reduced.